what happened to Hume's money theory

hallow everybody:
i'm reading Schumpeter's "history of economic analysis" recently.I
have a question.
Schumpeter said that "Hume stated the famous relationship between
changes in the money supply and the general price level;a relationship
which remained substantially unchallenged until the 1920s. "
What I want to know is that what happend to the above theory since the
1920s ?
I'll be glad to hear your response!
.